1. Field of the Invention
The present invention relates to a method of gasifying organic materials (carbonaceous compounds) such as coal, waste oil or shredded waste tire into gaseous fuel, carbon monoxide and hydrogen, and an apparatus therefor.
2. Description of the Related Art
Gasification of liquid wastes such as waste oil or waste organic solvent and solid organic materials such as coal or shredded waste tire means converting carbon and hydrogen contained in the organic materials into fuel gases, carbon monoxide and hydrogen gas (generally called syngas). Since gasification is endothermic reaction requiring continuous supply of heat, the gasification furnace should be kept at a high temperature sufficient to continue the reaction.
In the conventional method of gasification, the gasification furnace is kept at a high temperature by means of combustion heat generated from the oxidation reaction of organic materials supplied for gasification with oxygen. Further, in the state of high temperature sufficient to gasification reaction, steam or water is supplied to promote gasification and increase the concentration of hydrogen in the produced syngas.
FIGS. 1a to 1c illustrate schematically the mechanism of conventional system applied to gasification reactor for coal; FIGS. 1a, 1b and 1c indicate static floor type, fluid floor type, and flush fluid floor type, respectively. Coal, a sort of organic material, is typically gasified by one of the three conventional methods according to its size. Each method differs in supplying coal, oxygen and steam, and in discharging gases produced from gasification reaction and remained ash, while the reaction carried out in the gasification reactor is identical with each other. Generally, static floor type is applied to natural coal lumps, fluid floor type is to coal of several millimeter sizes, and flush fluid floor type is to coal of scores of micrometer sizes.
U.S. Pat. No. 6,120,567 (Sep. 19, 2000) describes a heating system for producing heat by the gasification of solid, organic biomass materials. In the method, the organic materials in a primary oxidation chamber of the catalytic type are gradually heated in a deficiency of oxidation to produce a gaseous combustible effluent, which is further oxidized to a fully oxidized state by burning in a secondary oxidation chamber.
U.S. Pat. No. 6,084,147 (Jul. 4, 2000) discloses a method for decomposing waste material contaminated with metal ions, wherein decomposition takes place quickly by injecting a steam/oxygen mixture into a fluidized bed of ceramic beads. In this method, the fluidizing gas mixture agitates the beads that then help to break up solid wastes, and the oxygen allows some oxidation to offset the thermal requirements of drying, pyrolysis, and steam reforming. Most of the pyrolysis takes place in the first stage, setting up the second stage for completion of pyrolysis and adjustment or gasification of the waste form using co-reactants to change the oxidation state of inorganics and using temperature to partition metallic wastes.
Further, U.S. Pat. No. 6,001,144 (Dec. 14, 1999) describes a process of gasifying waste containing organic substances which may be combusted or gasified by means of partial oxidation in the presence of air or oxygen and steam. The gasification process includes the step of adjusting the molar ratio of steam/carbon (H2O/C) for supplied steam and the organic substances containing carbon to be substantially between 1 and 10, partially oxidizing the organic substances at a temperature substantially between 700 and 900xc2x0 C., and discontinuing the supply of steam while continuing to supply air or oxygen to combust the remaining combustibles having carbon as their major component.
Since gasification is endothermic reaction, the reactor is required to be kept at a high temperature about 1,300xc2x0 C. for continuing the reaction. In conventional gasification methods, oxygen is supplied with organic materials (xe2x80x94CH2) to the gasification reactor, thereby inducing oxidation of carbon and hydrogen components in the organic materials and producing combustion heat from the oxidation to maintain such high temperature required to the gasification in the reactor. The oxidation reaction is indicated as follows:
C+O2xe2x86x92CO2xe2x80x83xe2x80x83(1)
2(xe2x80x94CH2)+3O2xe2x86x922H2O+2CO2xe2x80x83xe2x80x83(2)
Reaction 1 indicates the combustion reaction usually occurred in coal whose main component is carbon, and Reaction 2 is the main combustion reaction occurred in organic materials such as waste oil.
The requirement of oxygen, which varies with the aspect of coal (C) or waste oil (xe2x80x94CH2) supplied into the reactor, amounts to 0.5xcx9c1.0 weight of the coal or waste oil. The oxygen supplied into the reactor is consumed according to the Reaction 1 and 2 to increase the temperature in the reactor and produce combustion products, H2O and CO2.
The combustion products undergo gasification reaction with carbon, which is main component of the organic materials, as indicated in Reactions 3 and 4. The gasification reaction requires longer reaction time as compared with combustion reaction and higher temperature to continue the reaction. The gasification reactions of organic materials such as waste oil (xe2x80x94CH2) are indicated as Reactions 5 and 6.
C+H2Oxe2x86x92CO+H2xe2x80x83xe2x80x83(3)
C+CO2xe2x86x922COxe2x80x83xe2x80x83(4)
(xe2x80x94CH2)+H2Oxe2x86x92CO+2H2xe2x80x83xe2x80x83(5)
(xe2x80x94CH2)+CP2xe2x86x922CO+H2xe2x80x83xe2x80x83(6)
While the Reactions 1 and 2 are oxidation reaction, the Reactions 3 to 6 are reduction reaction. The gas produced from the reactions is fuel gas whose main components are CO and H2.
In conventional gasification methods, gasification reaction (Reactions 3 to 6) uses oxidation reaction (Reactions 1 and 2) which is induced by oxygen supplied with coal or waste oil for increasing the temperature of the gasification reactor. Further, additional supply of steam of high temperature is required to increase the concentration of hydrogen through water gas shift reaction (Reaction 7). The steam is acquired by means of heat exchange with fuel gas of high temperature in the boiler installed for cooling the fuel gas in the gasification reactor.
CO+H2Oxe2x86x92H2+CO2xe2x80x83xe2x80x83(7)
As described in the above, in conventional gasification methods, oxidation reaction (Reactions 1 and 2), reduction reaction (Reactions 3 to 6) and water gas shift reaction (Reaction 7) occur concurrently in the same space, and therefore, the production of hydrogen gas is low and secondary pollution usually occurs.
To solve the above problems, it is an object of the present invention to provide a method of gasifying organic materials (carbonaceous compounds) such as coal, shredded waste tire or waste oil into gaseous fuel, carbon monoxide and hydrogen, which facilitates the control of temperature in the gasification reactor as well as produces fuel gas of high quality by increasing the concentration of hydrogen.
It is another object of the present invention to provide an apparatus for the gasification method as described above.
To accomplish the above object, the present invention provides a method of gasifying organic materials (carbonaceous compounds) comprising the steps of:
supplying initial fuel gas and oxygen into a gasification reactor to produce water and carbon dioxide;
supplying the organic materials into the reactor and reacting them with the water and carbon dioxide to produce carbon monoxide and hydrogen gas;
discharging the carbon monoxide and hydrogen gas from the reactor;
recycling a part of the carbon monoxide and hydrogen gas discharged from the reactor into the reactor; and
reacting the carbon monoxide and hydrogen gas supplied into the reactor with oxygen to produce water and carbon dioxide.
The method of the present invention may comprise further the step of reacting the water and carbon dioxide, that is produced from the recycled carbon monoxide and hydrogen gas, with the organic materials to produce further carbon monoxide and hydrogen gas.
In this method, the oxygen is preferable to be supplied into the gasification reactor as the least amount as is required to maintain the temperature at about 1,300xc2x0 C. in the reactor, and the carbon monoxide and hydrogen gas is preferable to be supplied into the gasification reactor as the amount as is required to consume the oxygen completely in the reactor.
Specifically, the method of gasifying organic materials of the present invention comprises the steps of:
heating a gasification reactor to a temperature sufficient to gasify the organic materials;
supplying initial fuel gas and oxygen into the reactor to produce water and carbon dioxide with heat;
supplying the organic materials into the reactor and reacting them with the water and carbon dioxide to produce carbon monoxide and hydrogen gas;
discharging the carbon monoxide and hydrogen gas from the reactor;
recycling a part of the carbon monoxide and hydrogen gas discharged from the reactor into the reactor;
reacting the carbon monoxide and hydrogen gas supplied into the reactor with oxygen to produce water and carbon dioxide with heat; and
reacting the water and carbon dioxide with the organic materials to produce carbon monoxide and hydrogen gas.
To accomplish another object of the present invention, it is provided an apparatus for gasifying organic materials (carbonaceous compounds) comprising:
a gasification reactor for gasifying the organic materials into carbon monoxide and hydrogen gas;
a means for supplying the organic materials into the reactor;
a means for supplying oxygen into the reactor;
a means for discharging the carbon monoxide and hydrogen gas from the reactor; and
a means for recycling a part of the carbon monoxide and hydrogen gas discharged from the reactor into the reactor.
The gasification reactor may have two parts of the same shape and size which are connected each other vertically.
Further, each of the means for supplying oxygen and the means for recycling a part of the carbon monoxide and hydrogen gas may have at least two nozzles arranged on the wall of the reactor at a tangential direction.
In the present invention, by means of recycling the carbon monoxide and hydrogen gas produced from the gasification reaction of the organic materials into the gasification reactor, the recycled gases are oxidized with oxygen to produce H2O and CO2 and maintain the reactor at high temperature. More specifically, in order to make the condition of high temperature required for gasification reaction and to supply steam for increasing the concentration of hydrogen in the fuel gas (CO and H2) produced from the gasification reaction, a part of the fuel gas (mainly composed of CO and H2) produced from the gasification reaction is recycled into the gasification reactor, and then reacts with appropriate amount of oxygen, which then produces lots of heat, H2O and CO2. The heat is used for maintaining the gasification reactor at high temperature of about 1,300xc2x0 C. and H2O and CO2 gases are converted into H2 and CO by the reduction reaction with the organic materials. That is, in the present invention, the temperature of the gasification reactor elevates sufficiently for the gasification reaction, and then H2O and CO2 produced from the combustion react with the organic materials to produce fuel gas as well as high temperature required for gasification, all of which facilitate the control of temperature in the gasification reactor and result in the production of fuel gas of high quality by increasing the concentration of hydrogen.